1. Field of the Invention
The invention relates to what is called a lens-fitted film unit which is a single-use camera with a pre-loaded film, and, more particularly, to a lens-fitted film unit equipped with a film winding mechanism for rapid film winding.
2. Description of Related Art
A lend-fitted film unit with a film pre-loaded and a simple exposure mechanism incorporated therein, which is well known as a single-use or disposable camera, has been manufactured and marketed by the assignee of the present application. There are a variety of lens-fitted film units with a plastic film container such as a patrone or cartridge.
Such a lens-fitted film unit typically comprises a cartridge receiving chamber in which a film cartridge is pre-loaded and a film receiving chamber into which substantially the entire length of an unexposed filmstrip factory pre-wound out of the cartridge is received in a roll, these chambers being located at opposite ends of an exposure mechanism including a taking lens. One of the structural features of the lens-fitted film unit is a curved film passage between the film cartridge receiving chamber and the film receiving chamber to place the film in a concave focal plane. Film winding is performed for every exposure by rotating a winding knob engaged with a spool of the cartridge atop the film cartridge receiving chamber to wind exposed frames into the film cartridge frame by frame.
One of the film cartridges contains a roll of film having at most 40 frames for exposure. This 40 exposures film cartridge is equipped with a spool whose outer diameter is 7 mm. When a fresh lens-fitted film unit is used, the winding knob is rotated to advance and place the first frame into the exposure aperture and, by means of the film advancement, to charge a shutter drive mechanism and resetting a film counter. After exposure of the last frame, the winding knob is rotated until the entire length of the film strip is completely wound into the cartridge so that the film cartridge can be taken out of lens-fitted film unit in the light.
At the leading and trailing portions at opposite ends of the exposable portion, the film strip has several frames unusable for exposure but used for other purposes, for example, film processing. In the case where the lens-fitted film unit with a film cartridge pre-loaded therein, the winding knob is necessarily operated by approximately 1.25 turns, i.e. 450 degrees, in order to set the first frame in position and approximately 3.8 turns, i.e. 1,360 degrees, in order to completely wind up the entire length of film strip into the cartridge after exposure of the last frame.
When the winding mechanism is designed and adapted to permit the winding knob to be rotated 113 degrees by a single operation, it is necessary to turn the winding knob 4 times of operation before setting the first frame in the exposure aperture and 12 times operation until winding up the film strip completely into the cartridge after exposure of the last frame, which is troublesome and always imposes a burden on the user. In some types of the conventional cameras which are designed and adapted to allow the user to load a film roll easily, a step-up gear train is incorporated between a winding knob or winding lever and a spool of a film cartridge to transmit an increased speed of rotation from the winding knob to the spool. This kind of step-up gear train is, however, generally too bulky to be applied to the lens-fitted film unit one of whose features is to be small in size and compact in structure.